- Power supply derating reduces output capacity under high temperature, altitude, or poor cooling conditions.
- Derating helps prevent overheating and protects internal components from thermal stress.
- Always check the manufacturer’s derating curve before sizing an industrial power supply.
- Proper derating improves reliability, efficiency, and service life.
Industrial power supplies are rarely installed in ideal conditions. They often operate inside crowded control cabinets, near heat-generating equipment, or in factories where temperatures fluctuate throughout the day. Under these conditions, a power supply cannot always deliver its full rated output.
This is where power supply derating becomes essential. Understanding how derating works helps you choose the right industrial power supply, prevent unexpected downtime, and extend the service life of your equipment.
What Is Power Supply Derating?
Power supply derating is the intentional reduction of a power supply’s maximum output capacity when operating conditions become less favorable than the manufacturer’s rated conditions.
For example, an industrial power supply may be rated to deliver 480 W at an ambient temperature of 40°C. Once the surrounding temperature rises to 60°C, the manufacturer may specify that the maximum continuous output should be reduced to 384 W. Operating above this limit increases internal temperatures beyond the components’ safe operating range.
Derating is not a defect or limitation. It is a design practice that protects electronic components from excessive thermal stress while maintaining stable performance.
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Why Industrial Power Supplies Require Derating
High Ambient Temperatures
The most common factor leading to derating is temperature. All electrical power supplies will always convert some amount of electrical energy into heat. As the ambient temperature increases, the ability of the supply to dissipate the heat produced decreases. Excess temperatures can lead to thermal shut down.
Limited Ventilation
Most industrial power supplies are normally placed in enclosed electrical enclosures, making them prone to trapping heat. Other components in the enclosure produce extra heat. This heat can increase the temperature in the enclosure beyond the ambient temperature by a very large margin. Therefore, derating is necessary to control this problem.
High Altitude Installation
As the height increases, the density of air reduces. Considering that industrial power supplies use air to dissipate heat, thin air becomes unable to dissipate the heat. For this reason, manufacturers will indicate the output reduction once the installation reaches a certain height.
This aspect is vital for mining activities, mountain-related constructions, renewable energy plants, and industries that are at high altitudes.
Continuous Full-Load Operation
Operating an industrial power supply at 100 percent output continuously allows little margin for variation in temperature and temporary overload. Such factors cause thermal stress leading to reduced lifetimes. Derating allows management of electrical and mechanical stresses in addition to extending the power supply’s lifetime.
Factors That Affect Industrial Power Supply Derating
Ambient Temperature
The manufacturer indicates the temperature range within which the power supply operates at maximum output. Beyond the specified range, there is a reduction in the allowable output proportionally.
It is imperative to monitor the temperature near the power supply instead of just room temperature since the cabinet temperatures are usually higher.
Installation Altitude
Increasing elevation decreases the efficiency of cooling. The altitude derating of many industrial power supplies starts at about 2,000 meters, though there are some differences among various manufacturers. Before selecting the equipment for installation at an elevated location, confirm the altitude ratings provided by the supplier.
Airflow and Cooling Conditions
There is a direct relation between air circulation and heat dissipation. Restricted air circulation may be caused by a close placement of cabinets, obstructed ventilation holes or accumulated dust. Even high-quality industrial power supply can overheat due to insufficient air circulation.
Mounting Orientation
The industrial power supplies are intended for heat dissipation in certain installation positions. Mounting the unit horizontally if vertical mounting is required may decrease cooling and lead to derating. It is important to install the power supply in the position indicated by the manufacturer.
Input Voltage Variations
Unstable input voltage variations can cause additional heating. Industrial environment that features unstable power supply may add extra load to the industrial power supply especially during peak hours of electricity consumption. Wide input voltage range will help increase the stability of operation.
Load Type
Not every electrical load behaves the same.
- Resistive loads generally produce stable current demand.
- Inductive loads, such as motors, solenoids, and contactors, often generate high inrush currents during startup.
- Capacitive loads can also create significant charging currents that temporarily exceed steady-state operating values.
When selecting an industrial power supply, consider both continuous load requirements and transient current demands.
How to Read a Power Supply Derating Curve
One of the most valuable resources in a manufacturer’s datasheet is the derating curve. A derating curve illustrates how much output power remains available as operating conditions change. For temperature derating, the horizontal axis usually represents ambient temperature, while the vertical axis indicates the maximum allowable output percentage.
For example:
- Up to 50°C: 100% rated output
- 60°C: 80% rated output
- 70°C: 60% rated output
Although these values vary by model, the concept remains the same. Altitude derating curves work similarly by showing how output capacity decreases as installation elevation increases. Understanding these graphs allows you to size power supplies correctly before installation rather than troubleshooting overheating problems later.
How to Calculate the Required Derating for an Industrial Power Supply
Step 1: Determine Maximum Ambient Temperature
Measure the highest expected temperature around the installed power supply, not just the factory’s air-conditioned room. Electrical cabinets can easily operate 10–20°C warmer than the surrounding environment. If you do not get this accurate, every other calculation will be built on inaccuracy.
Step 2: Identify Installation Altitude
Confirm the site’s elevation above sea level. If the installation exceeds the manufacturer’s specified altitude limit, include altitude derating in your calculations. If you don’t identify this, then it means you’re overestimating what your supply can actually handle. This can have a negative effect on connected equipment.
Step 3: Calculate Actual Load Demand
Add together the continuous power consumption of all connected equipment. Include a realistic assessment of startup currents, future system expansion, and expected operating conditions. If you don’t calculate the actual load demand, this can lead to oversizing or undersizing. While the former leads to wasted budget, the latter leads to electrical faults.
Step 4: Apply the Manufacturer's Derating Curve
Using the manufacturer’s datasheet, determine how much usable output remains under your operating conditions. Never estimate or assume derating values. This can lead to inaccuracies which would affect how electricity flow to connected equipment.
Step 5: Select the Correct Power Supply Capacity
Choose a power supply that can comfortably support the required load after derating has been applied. This approach provides additional reliability while reducing thermal stress throughout the product’s operating life.
What Happens If You Ignore Power Supply Derating?
- Overheating: Internal temperatures rise beyond safe operating limits, accelerating wear on electronic components.
- Output voltage instability: Excessive heat can reduce voltage regulation accuracy, affecting sensitive industrial control equipment.
- Thermal shutdown: Many industrial power supplies include thermal protection that automatically shuts down the unit to prevent permanent damage. While this protects the hardware, it also stops production until temperatures return to normal.
- Reduced efficiency: Higher operating temperatures generally decrease efficiency, increasing energy consumption and additional heat generation.
- Premature component aging: Electrolytic capacitors, semiconductors, and magnetic components all experience shorter service lives when exposed to elevated temperatures for extended periods.
- Unexpected equipment downtime: A failed power supply often affects an entire control system. The resulting production interruptions can cost far more than selecting the correct power supply during the design stage.
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Conclusion
Power supply derating is essential for ensuring reliable, long-term performance in industrial applications. Need help selecting the right industrial power supply? Contact the experts at Anssin Electric for tailored recommendations and high-quality power solutions designed to perform reliably in demanding operating environments.
FAQs
Power supply derating will not be applicable all the time because it strictly depends on your operating environment and installation conditions. It is only necessary for you to derate your power supply when dealing with such extreme conditions as high ambient temperatures, high altitude, and low input line voltages.
If your power supply is working in a normal environment that involves a standard nominal room temperature, correct positioning, standard sea level air density, and standard input voltage, there is no problem for you to utilize the maximum rated capacity.
Most industrial power supplies usually start their derating procedure at ambient temperatures above +50°C or +60°C. Above those temperatures, the device will gradually lower its maximum output power in order to avoid overheating.
In order to keep your power supply working efficiently, do not fill it with your load fully. Leave at least 20% to 30% more than your total power consumption; 20% for normal conditions and 50% for the peak loads.
No, because the altitude is not always a reason for the derating. Only the power or capacity should be reduced in case if the altitude goes beyond certain low elevation values of 1,000 m (3,300 ft) or 2,000 m (6,560 ft) depending on the equipment requirements.